Click here to see a full size version of this map. Graphic: Sarah Butrymowicz

Earlier this summer, we published a map of high school graduation rates by district across the United States. We’re now breaking it down and exploring trends in different states and regions.

When I started working on our map of high school graduation rates, I thought it would be easy — or at the very least possible — to get this information for every district in the country. And so it was with some reluctance that I ultimately published something with glaring white, dataless spots, most notably all of Pennsylvania and Oklahoma. The truth is, despite having a national standard for calculating graduation rates, having the entire map colored in would be impossible. Here’s why:

— Many districts that aren’t shaded in simply don’t have a high school. Take New Hampshire, which had a lot of missing information in the northern part of the state. Students who live in those white districts are bused elsewhere for high school.

— Individual states can choose to suppress, or not publish, information for places where the student population is too small, based on a cutoff that they have set. For example, both Arizona and Nebraska told me that’s what happened with their missing districts. It’s common for states to suppress test score data for small districts for the same reason.

Related: The graduation rates from every school district* in one map

The theory is that student data is supposed to be vague enough that the public can’t identify individual students. But if a class of students is very small, the information might be enough to determine who got a certain test score or didn’t graduate. Let’s say eight students start in ninth grade, and six graduate four years later. It might not be hard to figure out who those two dropouts are.

— Regarding the biggest gaps in this map, in Pennsylvania and Oklahoma: Pennsylvania only releases a statewide graduation rate and graduation rates for individual schools. Without the exact number of graduates from each school, it’s impossible to accurately figure out a district rate.

Oklahoma does have this data. But I was told the state board of education needs to approve its release. I will update the map if we get that clearance.

Keep checking back as we examine other regions of the United States in the weeks to come, and tell us places you want to see covered in the comments or on Twitter: @sarahbutro or @hechingerreport.

[Cross-posted at The Hechinger Report]

Sarah Butrymowicz

Sarah Butrymowicz received a bachelor's degree from Tufts University and an M.S. from the Columbia University Graduate School of Journalism.